testfft.js

// $JSSHELL -j -f dsp.js -f testfft.js

FFT.prototype.compile = function() {

  // Locally scope variables for speed up
  var bufferSize      = this.bufferSize,
      cosTable        = this.cosTable,
      sinTable        = this.sinTable,
      reverseTable    = this.reverseTable;

  var forwardCode = "(function(buffer) {\n" +
    "if(buffer.length!==" + bufferSize+")throw\"incorrect buffer length\";\n";

  var initVars = [];
  for(var i=0;i<bufferSize;++i) {
    initVars.push("i" + i + "=buffer[" + reverseTable[i] + "]");
    initVars.push("r" + i + "=0");
  }
  forwardCode += "var " + initVars.join(",") + ";\n";

  var halfSize = 1, 
      phaseShiftStepReal, 
      phaseShiftStepImag, 
      currentPhaseShiftReal, 
      currentPhaseShiftImag, 
      off, 
      tmpReal, 
      i;

  forwardCode += "var tr, ti; \n";
  while ( halfSize < bufferSize ) {
    phaseShiftStepReal = cosTable[halfSize];
    phaseShiftStepImag = sinTable[halfSize];
    currentPhaseShiftReal = 1;
    currentPhaseShiftImag = 0;

    for ( var fftStep = 0; fftStep < halfSize; fftStep++ ) {
      i = fftStep;

      while ( i < bufferSize ) {
        off = i + halfSize;
        forwardCode += "tr=("+currentPhaseShiftReal+"*r"+off+")-("+currentPhaseShiftImag+"*i"+off+");";
        forwardCode += "ti=("+currentPhaseShiftReal+"*i"+off+")+("+currentPhaseShiftImag+"*r"+off+");";
        forwardCode += "r"+off+"=r"+i+"-tr;i"+off+"=i"+i+"-ti;r"+i+"+=tr;i"+i+"+=ti;\n";

        i += halfSize << 1;
      }

      tmpReal = currentPhaseShiftReal;
      currentPhaseShiftReal = (tmpReal * phaseShiftStepReal) - (currentPhaseShiftImag * phaseShiftStepImag);
      currentPhaseShiftImag = (tmpReal * phaseShiftStepImag) + (currentPhaseShiftImag * phaseShiftStepReal);
    }

    halfSize = halfSize << 1;
  }

  forwardCode += "var real=this.real,imag=this.imag,spectrum=this.spectrum,sqrt=Math.sqrt;\n";
  for(i=0;i<bufferSize;++i) {
    forwardCode += "real["+i+"]=r"+i+";imag["+i+"]=i"+i+";";
  }
  forwardCode += "\n";
 
  i = bufferSize/2;
  while(i--) {
    forwardCode += "spectrum["+i+"]=2*sqrt(r"+i+"*r"+i+"+i"+i+"*i"+i+")/"+bufferSize+";";
  }
  forwardCode += "\nreturn spectrum;})";

  this.forward = eval(forwardCode);
};

// sine signal at 440hz, sample rate=44100 
var buffer = new Float32Array(2048);
for(var i=0;i<buffer.length;++i) {
  buffer[i] = Math.sin(i * 2 * Math.PI * 440 / 44100);
}

var fft = new FFT(2048, 44100);
fft.compile();

var startTime = new Date().valueOf(), iterations=100;
for(var k=0;k<iterations;++k) {
  fft.forward(buffer);
}
var endTime = new Date().valueOf(), duration = endTime - startTime;

print("interations: " + iterations + "; total dur: " + duration + "ms; per item: " + (duration / iterations) + "ms");